Astronomers have discovered the heavy element barium in the atmosphere of two ultra-hot gas giant exoplanets named WASP-76 b and WASP-121 b.
Simulation of iron rain on the night side of WASP-76 b. (Image: ESO).
The discovery of barium around the two exoplanets WASP-76 b and WASP-121 b marks the heaviest element ever found in the atmosphere of a planet orbiting a star outside our Solar System. This finding could reveal conditions surrounding these hot Jupiter exoplanets, which are massive gas giants that orbit close to their host stars and are often affected by tidal locking, with one side always facing the star and the other side facing into space. The close proximity means that hot Jupiters take only a few days to orbit their host stars and can reach temperatures exceeding 1,000 degrees Celsius.
WASP-76 b is an extremely unique example of a hot Jupiter. Previously, astronomers discovered that temperatures on its day side could reach up to 2,400 degrees Celsius, hot enough to vaporize iron and other metals. When blown to the cooler night side of WASP-76 b, the vaporized iron condenses and falls as “iron rain.” Even under such extreme and unusual conditions, researchers did not expect to find barium, an element 2.5 times heavier than iron, in the atmosphere of WASP-76 b or WASP-121 b.
“The puzzling question is why such a heavy element exists in the upper atmosphere of these exoplanets”, shared Tomás Azevedo Silva, the lead researcher from the University of Porto and the Institute of Astrophysics and Space Science in Portugal, in a statement from the European Southern Observatory (ESO). Silva and his team used several ESO telescopes in their research. They published their findings on October 13 in the journal Astronomy & Astrophysics.
The high gravitational pull of these planets led the research team to predict that heavy elements like barium would quickly sink to the lower layers of the atmosphere. They are unclear about the natural processes that lead to the presence of barium in the atmospheres of WASP-76 b or WASP-121 b. Astronomers employed a technique called spectroscopy to study the chemical composition of the exoplanets. This technique relies on the fact that elements absorb and emit light at specific frequencies. Therefore, when light from a star passes through a planet’s atmosphere, the elements within that atmosphere leave unique signatures.
Silva and his team used the ESPRESSO spectrograph at the Very Large Telescope in Chile to determine the atmospheric composition of WASP-76 b and WASP-121 b. In the future, they plan to continue using instruments like the ANDES spectrograph at the Extremely Large Telescope currently under construction in Chile, which will allow for the analysis of the atmospheres of both similar large planets and smaller ones outside our Solar System.
